1. Field of the Invention
The present invention relates to an apparatus and method for repairing a liquid crystal display panel, and more particularly, to an apparatus and method for repairing a liquid crystal display panel, which is capable of improving a yield thereof by darkening a bright point to minimize a defect ratio thereof.
2. Discussion of the Related Art
Generally, a liquid crystal display (LCD) device controls the light transmittance of a liquid crystal material in accordance with a video signal to display a picture. For this, the liquid crystal display device includes a liquid crystal display panel in which liquid crystal cells are arranged in a matrix configuration, and a drive circuit to drive the liquid crystal display panel.
The liquid crystal display device is divided into two main classes of a twisted nematic (TN) mode in which a vertical direction electric field is used and an in-plane switch (ISP) mode in which a horizontal direction electric field is used, in accordance with the electric field direction in which a liquid crystal material is driven.
In the TN mode the liquid crystal material is driven by a vertical electric field between a pixel electrode and a common electrode that are arranged to be opposite to each other on a lower substrate and an upper substrate respectively. The TN mode has an advantage in that its aperture ratio is big, but a disadvantage in that its viewing angle is small. In the IPS mode the liquid crystal material is driven by a horizontal electric field between the pixel electrode and the common electrode that are arranged in parallel in a lower substrate. The IPS mode has an advantage in that its viewing angle is big, but a disadvantage in that its aperture ratio is small.
FIG. 1 is a sectional view illustrating a liquid crystal display panel of TN mode of the related art.
Referring to FIG. 1, the related art TN mode liquid crystal display panel includes an upper array substrate (or a color filter array substrate) having a black matrix 4, a color filter 6, a common electrode 18, and an upper alignment film 8 that are sequentially formed on an upper substrate 2; a lower array substrate having a thin film transistor (hereinafter, referred to as “TFT”), a pixel electrode 16 and a lower alignment film 38 that are formed on a lower substrate 32; and a liquid crystal material 52 injected into an inner space between the upper array substrate and the lower array substrate.
On the other hand, the IPS mode liquid crystal display panel has the common electrode 18 formed on the lower substrate 32 and an overcoat layer (not shown) formed on the color filter 6 of the upper substrate 2, wherein the overcoat layer is for compensating the stepped difference of the color filter 6.
On the upper array substrate of the IPS mode liquid crystal display panel, the black matrix 4 is formed on the upper substrate 2 and corresponds to an area of gate lines and data lines (not shown) and a TFT area of the lower array substrate. The black matrix provides a cell area where a color filter 6 is to be formed. The black matrix 4 prevents light leakage and absorbs external light, thereby increasing contrast. The color filter 6 is formed to extend to the black matrix 4 and the cell area divided by the black matrix 4. The color filter 6 is formed by Red, Green and Blue to realize R, G and B colors. A common voltage is supplied to the common electrode 18 to control the movement of the liquid crystal material. A pattern spacer 13 maintains a cell gap between the upper array substrate and the lower array substrate.
The TFT on the lower array substrate includes a gate electrode 9 formed on the lower substrate 32 along with a gate line; semiconductor layers 14, 42 overlapping the gate electrode 9 with a gate insulating film 44 therebetween; and source/drain electrodes 40, 47 formed together with a data line (not shown) with the semiconductor layers 14, 42 therebetween. The TFT supplies a pixel signal to a pixel electrode 16 from the data line in response to a scan signal from the gate line. The pixel electrode 16 is in contact with the drain electrode 47 of the TFT with a passivation film 50 therebetween, wherein the passivation film 50 is formed of a transparent conductive material with high light transmittance. The upper and the lower alignment films 8 and 38 for aligning the liquid crystal material are formed by applying an alignment material such as polyimide and performing a rubbing process.
If a defect is generated at each thin film of the upper array substrate and the lower array substrate of the related art liquid crystal display panel, a repair is performed by rework or using a laser. However, if a particle is soundly settled between the thin films of both the upper array substrate and the lower array substrate, it becomes impossible to do the repair by rework or laser.
FIG. 2 is a sectional view for explaining an alignment defect caused by airborne particles, and FIG. 3 is a photo representing a bright point caused by the particle upon realizing a picture.
Generally, in processes of manufacturing a liquid crystal display panel, it is possible for particles to settle between their films. For example, particles may settle on the panel in the chamber within which a designated thin film is formed, or if the panel is moved to a separate chamber or a third location to form another thin film, while the panel is being moved. An example of a particle 55 between the common electrode 18 and the upper alignment film 8 is illustrated in FIG. 2. In this example the alignment film corresponding to the particle 55 is not uniformly rubbed in a rubbing process, thereby generating a non-uniform alignment area A. Further, a portion of the color filter is separated by a defect on the process upon forming the color filter. Such particles 55 intermixed between layers may occur frequently causing various problems in the LCD panel.
For example, the non-uniform alignment area A causes light leakage in the liquid crystal display panel, and such light leakage interferes with light transmittance of the liquid crystal material. The light leakage appears as a bright point in the liquid crystal display panel, as illustrated in FIG. 3. Generally, a dark point is an area appearing dark in case of realizing a high gray, and a bright point is an area appearing bright in case of realizing a low gray. Herein, human eyes are more sensitive to a bright point than a dark point, thus a stricter standard is provided for a bright point defect than a dark point defect when determining if a panel is good or bad. Accordingly, a method is required to minimize a defect rate of a panel caused by a generation of a bright point.